Device-To-Device D2D Service Transmission Method, Apparatus, and Device

ABSTRACT

A method is provided. The method includes obtaining, by UE, signal quality of a first cell operating on a first transmission carrier frequency. When the UE determines that the signal quality of the first cell is higher than a preset threshold, and the UE receives first indication information sent by the first cell, the method includes selecting, by the UE, the first cell as a serving cell, where the first indication information indicates that the first cell can control the UE to transmit device-to-device D2D service data on a second transmission carrier frequency, and the first transmission carrier frequency and the second transmission carrier frequency are located at different frequencies.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of International Application No.PCT/CN2015/088640, filed on Aug. 31, 2015, the disclosure of which ishereby incorporated by reference in its entirety.

TECHNICAL FIELD

The present invention relates to the field of communicationstechnologies, and in particular, to a D2D service transmission method,apparatus, and device.

BACKGROUND

Currently, a Long Term Evolution (LTE) communications system is arelatively mainstream wireless communications technology. Adevice-to-device (D2D) technology is used as an important feature in3GPP LTE Release 12 and is standardized. D2D supports directcommunication between user terminals (User Equipment, UE). Usually, acell (referred to as a serving cell) providing a service for the UE canschedule a resource used for a D2D service only when a transmissioncarrier frequency of the serving cell selected by the UE and atransmission carrier frequency of the D2D service are located at a samefrequency. Correspondingly, when the transmission carrier frequency ofthe serving cell selected by the UE and the transmission carrierfrequency of the D2D service are located at different frequencies, theserving cell cannot provide D2D service transmission for the UE.

An application scenario of performing D2D service transmission when thetransmission carrier frequency of the serving cell selected by the UEand the transmission carrier frequency of the D2D service are located atdifferent frequencies is vehicle to vehicle (V2V) communication.

With continuous development of society, an intelligent transportationsystem advances continuously. A vehicle can obtain road statusinformation or receive an information service in time by using V2V. Asshown in FIG. 1, a vehicle may broadcast information, such as a speed ofthe vehicle, a traveling direction, a specific location, and whetheremergency braking is performed, to a surrounding vehicle by using theV2V communication. By obtaining such information, a driver can betterperceive a traffic status beyond a line of sight, so as to anticipate adanger and then dodge the danger. Information transmitted in a V2Vcommunications system is referred to as V2V information. In the V2Vcommunications system, a vehicle sends the V2V information to asurrounding vehicle in a broadcasting manner. A sending period isusually 1 to 10 Hz, and a volume of the V2V information approximatelyvaries from 50 to 1200 bytes.

A V2V communication scenario also belongs to direct communicationbetween user terminals. Therefore, a V2V service may be transmittedusing a D2D technology. However, a V2V service-specific transmissionfrequency may be different from a frequency of a current serving cell.In this case, an LTE-based Internet of Vehicles solution is as follows.A base station sends, to UE using a current serving cell of the UE,configuration information of a dedicated transmission carrier frequencyfor transmitting a V2V service. The UE sends a V2V service on thededicated transmission carrier frequency according to the configurationinformation by using the D2D technology.

Usually, the cell providing the service for the UE can schedule theresource used for the D2D service only when the transmission carrierfrequency of the serving cell selected by the UE and the transmissioncarrier frequency for the D2D service are located at a same frequency.However, in an LTE-based V2V communication scenario, a V2V-specifictransmission carrier frequency and an LTE control carrier frequency arelocated at two different frequencies. An existing mechanism for cellselection in the D2D service does not support resource allocation forthe V2V-specific transmission carrier frequency by using the LTE controlcarrier frequency.

SUMMARY

Embodiments provide a D2D service transmission method, apparatus, anddevice, to resolve a problem that a terminal cannot select atransmission carrier frequency located at a different frequency totransmit D2D service data.

According to a first aspect, a device-to-device (D2D) servicetransmission method is provided. The method includes obtaining, by UE,signal quality of a first cell operating on a first transmission carrierfrequency. When the UE determines that the signal quality of the firstcell is higher than a preset threshold, and the UE receives firstindication information sent by the first cell, the method also includesselecting, by the UE, the first cell as a serving cell. The firstindication information indicates that the first cell can control the UEto transmit device-to-device D2D service data on a second transmissioncarrier frequency, and the first transmission carrier frequency and thesecond transmission carrier frequency are located at differentfrequencies. The method also includes transmitting, by the UE, the D2Dservice data on the second transmission carrier frequency.

With reference to the first aspect, in a first possible implementationof the first aspect, that the UE receives first indication informationsent by the first cell includes: the UE receives the first indicationinformation that is sent by the first cell by broadcasting systeminformation; or the UE receives the first indication information that issent by the first cell by using radio resource control RRC-specificcontrol signaling.

With reference to the first aspect or the first possible implementationof the first aspect, in a second possible implementation of the firstaspect, before the UE receives the first indication information sent bythe first cell, the method further includes: sending, by the UE to thefirst cell, a request message including frequency information of atransmission carrier frequency for a D2D service in which the UE isinterested, so that the first cell sends the first indicationinformation according to the request message.

With reference to any one of the first aspect or the first to the secondpossible implementations of the first aspect, in a third possibleimplementation of the first aspect, the first indication informationincludes frequency information of a frequency of at least one secondtransmission carrier frequency.

With reference to the second or the third possible implementation of thefirst aspect, in a fourth possible implementation of the first aspect, afrequency of the second transmission carrier frequency is included inthe request message.

With reference to any one of the first aspect or the first to the fourthpossible implementations of the first aspect, in a fifth possibleimplementation of the first aspect, after the UE transmits a D2D serviceon the second transmission carrier frequency, the method furtherincludes: sending, by the UE to the first cell, a notification messageincluding frequency information of the second transmission carrierfrequency. The notification message is used to inform the first cellthat the UE uses the second transmission carrier frequency as atransmission carrier frequency for transmitting the D2D service.

With reference to any one of the first aspect or the first to the thirdpossible implementations of the first aspect, in a sixth possibleimplementation of the first aspect, after the UE transmits the D2Dservice on the second transmission carrier frequency, the method furtherincludes: performing, by the UE, frequency scanning on a thirdtransmission carrier frequency, to determine a second cell; when thesecond cell meets a specified condition, reselecting, by the UE, thesecond cell as the serving cell; and transmitting, by the UE, D2Dservice data on a transmission carrier frequency that is used to executea D2D service and that can be controlled by the second cell.

With reference to the sixth possible implementation of the first aspect,in a seventh possible implementation of the first aspect, the specifiedcondition includes at least one of the following: signal quality of thesecond cell is higher than or equal to a reselection threshold, and theUE can receive a second indication message sent by the second cell,where the second indication message indicates that the second cell cancontrol the UE to transmit the D2D service data on the secondtransmission carrier frequency; the signal quality of the first cell islower than an access threshold, signal quality of the second cell ishigher than or equal to a reselection threshold, and the UE can receivea second indication message sent by the second cell, where the secondindication message indicates that the second cell can control the UE totransmit the D2D service data on the second transmission carrierfrequency; or the signal quality of the first cell is lower than anaccess threshold, signal quality of the second cell is higher than orequal to a reselection threshold, and the UE can receive a thirdindication message sent by the second cell, where the third indicationmessage indicates that the second cell can control the UE to transmitthe D2D service data on the third transmission carrier frequency.

With reference to the sixth possible implementation of the first aspect,in an eighth possible implementation of the first aspect, the firstindication information further includes an access priority of atransmission carrier frequency used for transmitting the D2D service.The specified condition includes at least one of the following: signalquality of the second cell is higher than or equal to a reselectionthreshold, the UE can receive a third indication message sent by thesecond cell, and an access priority of the third transmission carrierfrequency is higher than that of the second transmission carrierfrequency, where the third indication message indicates that the secondcell can control the UE to transmit the D2D service data on the thirdtransmission carrier frequency; or the signal quality of the first cellis lower than an access threshold, signal quality of the second cell ishigher than or equal to a reselection threshold, the UE can receive athird indication message sent by the second cell, and an access priorityof the third transmission carrier frequency is higher than that of thesecond transmission carrier frequency, where the third indicationmessage indicates that the second cell can control the UE to transmitthe D2D service data on the third transmission carrier frequency.

With reference to the sixth possible implementation of the first aspect,in a ninth possible implementation of the first aspect, the firstindication information further includes a cell reselection priority. Thespecified condition includes at least one of the following: signalquality of the second cell is higher than or equal to a reselectionthreshold, a reselection priority of the second cell is higher than orequal to that of the first cell, and the UE can receive a secondindication message sent by the second cell, where the second indicationmessage indicates that the second cell can control the UE to transmitthe D2D service data on the second transmission carrier frequency; orsignal quality of the second cell is higher than the signal quality ofthe first cell, a reselection priority of the second cell is higher thanor equal to that of the first cell, and the UE can receive a secondindication message sent by the second cell, where the second indicationmessage indicates that the second cell can control the UE to transmitthe D2D service data on the second transmission carrier frequency.

According to a second aspect, a device-to-device D2D servicetransmission method is provided. The method includes sending, by a firstcell, first indication information using a first transmission carrierfrequency. The first indication information indicate that the first cellcan control UE to transmit device-to-device (D2D) service data on asecond transmission carrier frequency. The UE determines, according tothe indication information, to use the first cell as a serving cell andtransmit the D2D service data on the second transmission carrierfrequency. The first transmission carrier frequency and the secondtransmission carrier frequency are located at different frequencies.

With reference to the second aspect, in a first possible implementationof the second aspect, the method further includes: when the first celldetermines that the UE transmits the D2D service data on the secondtransmission carrier frequency, allocating, by the first cell, a D2Dtransmission resource on the second transmission carrier frequency tothe UE.

With reference to the second aspect or the first possible implementationof the second aspect, in a second possible implementation of the secondaspect, sending, by the first cell, first indication information using afirst transmission carrier frequency includes: sending, by the firstcell, the indication information by broadcasting system information; orsending, by the first cell, the first indication information by usingradio resource control RRC-specific control signaling.

With reference to any one of the second aspect or the first to thesecond possible implementations of the second aspect, in a thirdpossible implementation of the second aspect, before the sending, by afirst cell, first indication information using a first transmissioncarrier frequency, the method further includes: receiving, by the firstcell, a request message sent by the UE. The request message includesfrequency information of a transmission carrier frequency for a D2Dservice in which the UE is interested. The method also includes sending,by the first cell, the first indication information according to therequest message.

With reference to any one of the second aspect or the first to the thirdpossible implementations of the second aspect, in a fourth possibleimplementation of the second aspect, the first indication informationthat is sent by the first cell using the first transmission carrierfrequency includes frequency information of at least one secondtransmission carrier frequency.

With reference to the fourth possible implementation of the secondaspect, in a fifth possible implementation of the second aspect,frequency information that is of the second transmission carrierfrequency and that is in the first indication information sent by thefirst cell is included in the request message.

With reference to any one of the second aspect or the first to the fifthpossible implementations of the second aspect, in a sixth possibleimplementation of the second aspect, the method further includes:receiving, by the first cell, a notification message that includes thefrequency information of the second transmission carrier frequency andthat is sent by the UE. The notification message informs the first cellthat the UE uses the second transmission carrier frequency as atransmission carrier frequency for transmitting the D2D service data.

According to a third aspect, a device-to-device (D2D) servicetransmission apparatus is provided. The apparatus includes an obtainingmodule, configured to obtain signal quality of a first cell operating ona first transmission carrier frequency. The apparatus also includes areceiving module, configured to receive first indication informationsent by the first cell. The apparatus also includes a selection module,configured to, when it is determined that the signal quality of thefirst cell is higher than a preset threshold, and the first indicationinformation sent by the first cell is received, select the first cell asa serving cell. The first indication information indicates that thefirst cell can control UE to transmit device-to-device D2D service dataon a second transmission carrier frequency, and the first transmissioncarrier frequency and the second transmission carrier frequency arelocated at different frequencies. The apparatus also includes anexecution module, configured to transmit the D2D service data on thesecond transmission carrier frequency.

With reference to the third aspect, in a first possible implementationof the third aspect, the receiving module is configured to receive thefirst indication information that is sent by the first cell bybroadcasting system information, or receive the first indicationinformation that is sent by the first cell using radio resource control(RRC)-specific control signaling.

With reference to the third aspect or the first possible implementationof the third aspect, in a second possible implementation of the thirdaspect, the apparatus further includes a first sending module,configured to send, to the first cell, a request message includingfrequency information of a transmission carrier frequency for a D2Dservice in which the UE is interested. The first cell sends the firstindication information according to the request message.

With reference to any one of the third aspect or the first to the secondpossible implementations of the third aspect, in a third possibleimplementation of the third aspect, the first indication informationreceived by the receiving module includes frequency information of afrequency of at least one second transmission carrier frequency.

With reference to the second or the third possible implementation of thethird aspect, in a fourth possible implementation of the third aspect, afrequency of the second transmission carrier frequency selected by theselection module is included in the request message.

With reference to any one of the third aspect or the first to the fourthpossible implementations of the third aspect, in a fifth possibleimplementation of the third aspect, a second sending module isconfigured to send, to the first cell, a notification message includingfrequency information of the second transmission carrier frequency. Thenotification message informs the first cell that the UE uses the secondtransmission carrier frequency as a transmission carrier frequency fortransmitting the D2D service.

With reference to any one of the third aspect or the first to the thirdpossible implementations of the third aspect, in a sixth possibleimplementation of the third aspect, the apparatus further includes: adetermining module, configured to perform frequency scanning on a thirdtransmission carrier frequency, to determine a second cell. Theapparatus also includes a reselection module, configured to: when thesecond cell meets a specified condition, reselect the second cell as theserving cell. The apparatus also includes a transmission module,configured to transmit D2D service data on a transmission carrierfrequency that is used to execute a D2D service and that can becontrolled by the second cell.

With reference to the sixth possible implementation of the third aspect,in a seventh possible implementation of the third aspect, the specifiedcondition determined by the reselection module includes at least one ofthe following: signal quality of the second cell is higher than or equalto a reselection threshold, and the UE can receive a second indicationmessage sent by the second cell, where the second indication messageindicates that the second cell can control the UE to transmit the D2Dservice data on the second transmission carrier frequency; the signalquality of the first cell is lower than an access threshold, signalquality of the second cell is higher than or equal to a reselectionthreshold, and the UE can receive a second indication message sent bythe second cell, where the second indication message indicates that thesecond cell can control the UE to transmit the D2D service data on thesecond transmission carrier frequency; or the signal quality of thefirst cell is lower than an access threshold, signal quality of thesecond cell is higher than or equal to a reselection threshold, and theUE can receive a third indication message sent by the second cell, wherethe third indication message indicates that the second cell can controlthe UE to transmit the D2D service data on the third transmissioncarrier frequency.

With reference to the sixth possible implementation of the third aspect,in an eighth possible implementation of the third aspect, the firstindication information further includes an access priority of atransmission carrier frequency used for transmitting the D2D service.The specified condition determined by the reselection module includes atleast one of the following: signal quality of the second cell is higherthan or equal to a reselection threshold, the UE can receive a thirdindication message sent by the second cell, and an access priority ofthe third transmission carrier frequency is higher than that of thesecond transmission carrier frequency, where the third indicationmessage indicates that the second cell can control the UE to transmitthe D2D service data on the third transmission carrier frequency; or thesignal quality of the first cell is lower than an access threshold,signal quality of the second cell is higher than or equal to areselection threshold, the UE can receive a third indication messagesent by the second cell, and an access priority of the thirdtransmission carrier frequency is higher than that of the secondtransmission carrier frequency, where the third indication messageindicates that the second cell can control the UE to transmit the D2Dservice data on the third transmission carrier frequency.

With reference to the sixth possible implementation of the third aspect,in a ninth possible implementation of the third aspect, the firstindication information further includes a cell reselection priority. Thespecified condition determined by the reselection module includes atleast one of the following: signal quality of the second cell is higherthan or equal to a reselection threshold, a reselection priority of thesecond cell is higher than or equal to that of the first cell, and theUE can receive a second indication message sent by the second cell,where the second indication message indicates that the second cell cancontrol the UE to transmit the D2D service data on the secondtransmission carrier frequency; or signal quality of the second cell ishigher than the signal quality of the first cell, a reselection priorityof the second cell is higher than or equal to that of the first cell,and the UE can receive a second indication message sent by the secondcell, where the second indication message indicates that the second cellcan control the UE to transmit the D2D service data on the secondtransmission carrier frequency.

According to a fourth aspect, a device-to-device (D2D) servicetransmission apparatus is provided. The apparatus includes a sendingmodule, configured to send first indication information using a firsttransmission carrier frequency. The first indication informationindicates that the first cell can control UE to transmit D2D servicedata on a second transmission carrier frequency. The UE determines,according to the indication information, to use the first cell as aserving cell and transmit the D2D service data on the secondtransmission carrier frequency. The first transmission carrier frequencyand the second transmission carrier frequency are located at differentfrequencies.

With reference to the fourth aspect, in a first possible implementationof the fourth aspect, the apparatus further includes an executionmodule, configured to: when it is determined that the UE transmits theD2D service data on the second transmission carrier frequency, allocatea D2D transmission resource on the second transmission carrier frequencyto the UE.

With reference to the fourth aspect or the first possible implementationof the fourth aspect, in a second possible implementation of the fourthaspect, the sending module is configured to send the indicationinformation by broadcasting system information; or send the firstindication information using radio resource control RRC-specific controlsignaling.

With reference to any one of the fourth aspect or the first to thesecond possible implementations of the fourth aspect, in a thirdpossible implementation of the fourth aspect, the apparatus furtherincludes a first receiving module, configured to receive a requestmessage sent by the UE. The request message includes frequencyinformation of a transmission carrier frequency for a D2D service inwhich the UE is interested. The sending module is configured to send thefirst indication information according to the request message.

With reference to any one of the fourth aspect or the first to the thirdpossible implementations of the fourth aspect, in a fourth possibleimplementation of the fourth aspect, the first indication informationthat is sent by the sending module using the first transmission carrierfrequency includes frequency information of at least one secondtransmission carrier frequency.

With reference to the fourth possible implementation of the fourthaspect, in a fifth possible implementation of the fourth aspect,frequency information that is of the second transmission carrierfrequency and that is in the first indication information sent by thesending module is included in the request message.

With reference to any one of the fourth aspect or the first to the fifthpossible implementations of the fourth aspect, in a sixth possibleimplementation of the fourth aspect, the apparatus further includes asecond receiving module, configured to receive a notification messagethat includes the frequency information of the second transmissioncarrier frequency and that is sent by the UE. The notification messageinforms the first cell that the UE uses the second transmission carrierfrequency as a transmission carrier frequency for transmitting the D2Dservice data.

According to a fifth aspect, a device-to-device (D2D) servicetransmission device is provided. The device includes a processor,configured to obtain signal quality of a first cell operating on a firsttransmission carrier frequency. The device also includes an interface,configured to receive first indication information sent by the firstcell. The processor is further configured to, when it is determined thatthe signal quality of the first cell is higher than a preset threshold,and the first indication information sent by the first cell is received,select the first cell as a serving cell. The first indicationinformation indicates that the first cell can control UE to transmitdevice-to-device D2D service data on a second transmission carrierfrequency, and the first transmission carrier frequency and the secondtransmission carrier frequency are located at different frequencies. Theprocessor is further configured to transmit the D2D service data on thesecond transmission carrier frequency.

With reference to the fifth aspect, in a first possible implementationof the fifth aspect, the interface is configured to receive the firstindication information that is sent by the first cell by broadcastingsystem information; or receive the first indication information that issent by the first cell by using radio resource control (RRC)-specificcontrol signaling.

With reference to the fifth aspect or the first possible implementationof the fifth aspect, in a second possible implementation of the fifthaspect, the processor is further configured to send, to the first cellusing the interface, a request message including frequency informationof a transmission carrier frequency for a D2D service in which the UE isinterested. The first cell sends the first indication informationaccording to the request message.

With reference to any one of the fifth aspect or the first to the secondpossible implementations of the fifth aspect, in a third possibleimplementation of the fifth aspect, the first indication informationreceived by the interface includes frequency information of a frequencyof at least one second transmission carrier frequency.

With reference to the second or the third possible implementation of thefifth aspect, in a fourth possible implementation of the fifth aspect, afrequency of the second transmission carrier frequency selected by theprocessor is included in the request message.

With reference to any one of the fifth aspect or the first to the fourthpossible implementations of the fifth aspect, in a fifth possibleimplementation of the fifth aspect, the interface is further configuredto send, to the first cell, a notification message including frequencyinformation of the second transmission carrier frequency. Thenotification message informs the first cell that the UE uses the secondtransmission carrier frequency as a transmission carrier frequency fortransmitting the D2D service.

With reference to any one of the fifth aspect or the first to the thirdpossible implementations of the fifth aspect, in a sixth possibleimplementation of the fifth aspect, the processor is further configuredto: perform frequency scanning on a third transmission carrierfrequency, to determine a second cell. When the second cell meets aspecified condition, the processor is further configured to reselect thesecond cell as the serving cell. The processor is further configured totransmit D2D service data on a transmission carrier frequency that isused to execute a D2D service and that can be controlled by the secondcell.

With reference to the sixth possible implementation of the fifth aspect,in a seventh possible implementation of the fifth aspect, the specifiedcondition determined by the processor includes at least one of thefollowing: signal quality of the second cell is higher than or equal toa reselection threshold, and the UE can receive a second indicationmessage sent by the second cell, where the second indication messageindicates that the second cell can control the UE to transmit the D2Dservice data on the second transmission carrier frequency; the signalquality of the first cell is lower than an access threshold, signalquality of the second cell is higher than or equal to a reselectionthreshold, and the UE can receive a second indication message sent bythe second cell, where the second indication message indicates that thesecond cell can control the UE to transmit the D2D service data on thesecond transmission carrier frequency; or the signal quality of thefirst cell is lower than an access threshold, signal quality of thesecond cell is higher than or equal to a reselection threshold, and theUE can receive a third indication message sent by the second cell, wherethe third indication message indicates that the second cell can controlthe UE to transmit the D2D service data on the third transmissioncarrier frequency.

With reference to the sixth possible implementation of the fifth aspect,in an eighth possible implementation of the fifth aspect, the firstindication information further includes an access priority of atransmission carrier frequency used for transmitting the D2D service.The specified condition determined by the processor includes at leastone of the following: signal quality of the second cell is higher thanor equal to a reselection threshold, the UE can receive a thirdindication message sent by the second cell, and an access priority ofthe third transmission carrier frequency is higher than that of thesecond transmission carrier frequency, where the third indicationmessage indicates that the second cell can control the UE to transmitthe D2D service data on the third transmission carrier frequency; or thesignal quality of the first cell is lower than an access threshold,signal quality of the second cell is higher than or equal to areselection threshold, the UE can receive a third indication messagesent by the second cell, and an access priority of the thirdtransmission carrier frequency is higher than that of the secondtransmission carrier frequency, where the third indication messageindicates that the second cell can control the UE to transmit the D2Dservice data on the third transmission carrier frequency.

With reference to the sixth possible implementation of the fifth aspect,in a ninth possible implementation of the fifth aspect, the firstindication information further includes a cell reselection priority; andthe specified condition determined by the processor includes at leastone of the following: signal quality of the second cell is higher thanor equal to a reselection threshold, a reselection priority of thesecond cell is higher than or equal to that of the first cell, and theUE can receive a second indication message sent by the second cell,where the second indication message indicates that the second cell cancontrol the UE to transmit the D2D service data on the secondtransmission carrier frequency; or signal quality of the second cell ishigher than the signal quality of the first cell, a reselection priorityof the second cell is higher than or equal to that of the first cell,and the UE can receive a second indication message sent by the secondcell, where the second indication message indicates that the second cellcan control the UE to transmit the D2D service data on the secondtransmission carrier frequency.

According to a sixth aspect, a device-to-device (D2D) servicetransmission device is provided. The device includes a processor and aninterface. The processor is configured to send first indicationinformation based on a first transmission carrier frequency using theinterface. The first indication information indicates that the firstcell can control UE to transmit device-to-device (D2D) service data on asecond transmission carrier frequency. The UE determines, according tothe indication information, to use the first cell as a serving cell andtransmit the D2D service data on the second transmission carrierfrequency. The first transmission carrier frequency and the secondtransmission carrier frequency are located at different frequencies.

With reference to the sixth aspect, in a first possible implementationof the sixth aspect, the processor is further configured to: when it isdetermined that the UE transmits the D2D service data on the secondtransmission carrier frequency, allocate a D2D transmission resource onthe second transmission carrier frequency to the UE.

With reference to the sixth aspect or the first possible implementationof the sixth aspect, in a second possible implementation of the sixthaspect, the interface is configured to send the indication informationby broadcasting system information; or send he first indicationinformation using radio resource control (RRC)-specific controlsignaling.

With reference to any one of the sixth aspect or the first to the secondpossible implementations of the sixth aspect, in a third possibleimplementation of the sixth aspect, the interface may be furtherconfigured to receive a request message sent by the UE. The requestmessage includes frequency information of a transmission carrierfrequency for a D2D service in which the UE is interested; and send thefirst indication information according to the request message.

With reference to any one of the sixth aspect or the first to the thirdpossible implementations of the sixth aspect, in a fourth possibleimplementation of the sixth aspect, the first indication informationthat is sent based on the first transmission carrier frequency by usingthe interface includes frequency information of at least one secondtransmission carrier frequency.

With reference to the fourth possible implementation of the sixthaspect, in a fifth possible implementation of the sixth aspect, thefrequency information that is of the second transmission carrierfrequency and that is in the first indication information sent by theinterface is included in the request message.

With reference to any one of the sixth aspect or the first to the fifthpossible implementations of the sixth aspect, in a sixth possibleimplementation of the sixth aspect, the interface is further configuredto receive a notification message that includes the frequencyinformation of the second transmission carrier frequency and that issent by the UE. The notification message informs the first cell that theUE uses the second transmission carrier frequency as a transmissioncarrier frequency for transmitting the D2D service data.

According to the foregoing technical solutions, the UE obtains thesignal quality of the first cell operating on the first transmissioncarrier frequency. When the UE determines that the signal quality of thefirst cell is higher than the preset threshold, and the UE receives thefirst indication information sent by the first cell, the UE selects thefirst cell as the serving cell, and transmits the D2D service data onthe second transmission carrier frequency. By receiving the firstindication information, the UE can select a transmission carrierfrequency located at a different frequency to transmit the D2D service,so as to resolve a problem that the terminal cannot select atransmission carrier frequency located at a different frequency totransmit the D2D service data.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawings, in which:

FIG. 1 is a schematic diagram of V2V communication in accordance withembodiments of the present invention;

FIG. 2a is a flowchart of a D2D service transmission method proposed inEmbodiment 1 of the present invention;

FIG. 2b is a flowchart of a D2D service transmission method proposed inEmbodiment 2 of the present invention;

FIG. 3 is a schematic structural diagram of a D2D service transmissionapparatus proposed in Embodiment 2 of the present invention;

FIG. 4 is a schematic structural diagram of a D2D service transmissiondevice proposed in Embodiment 2 of the present invention;

FIG. 5 is a flowchart of a D2D service transmission method proposed inEmbodiment 3 of the present invention; and

FIG. 6 is a schematic structural diagram of a D2D service transmissionapparatus proposed in Embodiment 3 of the present invention.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

Usually, a terminal cannot select a transmission carrier frequencylocated at a different frequency to transmit D2D service data. In thetechnical solutions proposed in embodiments of the present invention, UEobtains signal quality of a first cell operating on a first transmissioncarrier frequency. When the UE determines that the signal quality of thefirst cell is higher than a preset threshold, and the UE receives firstindication information sent by the first cell, the UE selects the firstcell as a serving cell, and transmits the D2D service data on a secondtransmission carrier frequency. By receiving the first indicationinformation, the UE can select a transmission carrier frequency locatedat a different frequency to transmit a D2D service, so as to resolve aproblem that the terminal cannot select a transmission carrier frequencylocated at a different frequency to transmit the D2D service data.

The following describes, in detail with reference to the accompanyingdrawings, main implementation principles and specific implementations ofthe technical solutions of the embodiments of the present invention, andcorresponding achievable beneficial effects.

For ease of description, in the technical solutions proposed in theembodiments of the present invention, cells and transmission carrierfrequencies are distinguished, for example, respectively as a first celland a second cell, and a first transmission carrier frequency, a secondtransmission carrier frequency and a third transmission carrierfrequency. Correspondingly, for a terminal side, user terminals (userequipment, UE) are distinguished as first UE and second UE,respectively.

According to a D2D service transmission method proposed in embodimentsof the present invention, the UE obtains the signal quality of the firstcell operating on the first transmission carrier frequency. When the UEdetermines that the signal quality of the first cell is higher than thepreset threshold, and the UE receives the first indication informationsent by the first cell, the UE selects the first cell as the servingcell, and transmits the D2D service data on the second transmissioncarrier frequency.

The first indication information indicates that the first cell cancontrol the UE to transmit the D2D service data on the secondtransmission carrier frequency. The first transmission carrier frequencyand the second transmission carrier frequency are located at differentfrequencies.

The following describes, in detail with reference to the accompanyingdrawings, the main implementation principles and the specificimplementations of the technical solutions of the embodiments of thepresent invention, and the corresponding achievable beneficial effects.

Embodiment 1

Embodiment 1 of the present invention provides a D2D servicetransmission method. As shown in FIG. 2a , a specific processingprocedure of the method is described as follows.

Step 21: UE obtains signal quality of a first cell operating on a firsttransmission carrier frequency.

The UE measures signal quality of a cell, to obtain the signal qualityof the first cell operating on the first transmission carrier frequency.

Step 22: The first cell sends first indication information.

There is no fixed time sequence between step 22 and step 21. The firstcell may send the first indication information periodically or in ascheduled manner, or send the first indication information at any time.For ease of description, in the technical solution proposed inEmbodiment 1 of the present invention, step 22 is performed after step21.

The first cell may send the first indication information in thefollowing two manners.

In a first manner, the first cell sends the first indication informationby broadcasting system information.

In a second manner, the first cell sends the first indicationinformation using RRC-specific control signaling.

The first indication information indicates that the first cell cancontrol the UE to transmit D2D service data on a second transmissioncarrier frequency. The first transmission carrier frequency and thesecond transmission carrier frequency are located at differentfrequencies.

Optionally, before the first cell sends the first indication informationin step 22, the method further includes the following step.

The UE sends, to the first cell, a request message including frequencyinformation of a transmission carrier frequency for a D2D service inwhich the UE is interested. The first cell sends the first indicationinformation according to the received request message.

Specifically, frequency information that is of the second transmissioncarrier frequency and that is in the first indication information sentby the first cell is included in the request message.

Step 23: When the UE determines that the signal quality of the firstcell is higher than a preset threshold, and the UE receives theindication information sent by the first cell, the UE selects the firstcell as a serving cell.

Correspondingly, the UE may receive, in the following two manners, thefirst indication information sent by the first cell:

In a first manner, the UE receives the first indication information thatis sent by the first cell by broadcasting the system information.

In a second manner, the UE receives the first indication informationthat is sent by the first cell using the RRC-specific control signaling.

The UE selects the first cell as the serving cell, and the serving cellis a cell that can provide a D2D service.

Optionally, the first indication information includes a frequency of atleast one second transmission carrier frequency.

Step 24: The UE transmits D2D service data on a second transmissioncarrier frequency.

An LTE-based V2V communication scenario is used as an example fordetailed description.

The UE receives, using the first transmission carrier frequency, theindication information sent by the first cell. The UE determines thatthe first cell can control V2V service transmission on the secondtransmission carrier frequency. The UE measures the signal quality ofthe first cell, and determines, according to a measurement result,whether the signal quality of the first cell is higher than or equal tothe preset threshold. If a determining result indicates that the signalquality of the first cell is higher than or equal to the presetthreshold, the UE accesses and camps on the first cell. That is, the UEselects the first cell as the serving cell. The UE uses the secondtransmission carrier frequency indicated by the indication informationas a transmission carrier frequency for carrying a V2V service.

In the LTE-based V2V communication scenario, the transmission carrierfrequency for transmitting the V2V service and an LTE control carrierfrequency are located at two different frequencies. An existingmechanism for cell selection in a D2D service does not support resourceallocation for a V2V-specific transmission carrier frequency by usingthe LTE control carrier frequency. Based on this, in the technicalsolution proposed in Embodiment 1 of the present invention, the firstcell operating on the first transmission carrier frequency sends theindication information. When the UE determines, according to thereceived indication information, that the signal quality of the firstcell is higher than the preset threshold, the UE selects the first cellas the serving cell, and transmits the V2V service on the secondtransmission carrier frequency.

Optionally, after step 24, the method may further include the followingstep.

The UE sets a D2D service coverage identifier to a valid value.

In this case, the UE sets a D2D service coverage identifier of the UE toin-coverage. When being used as a synchronization source on the secondtransmission carrier frequency to send a synchronization signal, the UEmay have a higher synchronization source priority if the D2D servicecoverage identifier is set to in-coverage.

After the UE uses the first cell as the serving cell, the UE is notalways still. Therefore, as the UE moves, the UE may detect a secondcell whose signal quality is higher than that of the first cell, or theUE expects to transmit a D2D service using another transmission carrierfrequency. In this case, the UE needs to perform cell reselection.

Therefore, after the UE transmits the D2D service data on the secondtransmission carrier frequency in step 24, the method may furtherinclude the following step.

The UE reselects a second cell for access.

The UE performs frequency scanning on a third transmission carrierfrequency, to determine the second cell. When the second cell meets aspecified condition, the UE reselects the second cell as the servingcell. The UE transmits D2D service data on a transmission carrierfrequency that is used to execute a D2D service and that can becontrolled by the second cell.

The specified condition includes at least one of the following.

Condition 1: Signal quality of the second cell is higher than or equalto a reselection threshold, and the UE can receive a second indicationmessage sent by the second cell. The second indication message indicatesthat the second cell can control the UE to transmit the D2D service dataon the second transmission carrier frequency.

Condition 2: The signal quality of the first cell is lower than anaccess threshold, signal quality of the second cell is higher than orequal to a reselection threshold, and the UE can receive a secondindication message sent by the second cell. The second indicationmessage indicates that the second cell can control the UE to transmitthe D2D service data on the second transmission carrier frequency.

Condition 3: The signal quality of the first cell is lower than anaccess threshold, signal quality of the second cell is higher than orequal to a reselection threshold, and the UE can receive a thirdindication message sent by the second cell. The third indication messageindicates that the second cell can control the UE to transmit the D2Dservice data on the third transmission carrier frequency.

The first indication information further includes an access priority ofa transmission carrier frequency used for transmitting the D2D service.In this scenario, the specified condition includes at least one of thefollowing.

Condition 1: Signal quality of the second cell is higher than or equalto a reselection threshold, the UE can receive a third indicationmessage sent by the second cell, and an access priority of the thirdtransmission carrier frequency is higher than that of the secondtransmission carrier frequency. The third indication message indicatesthat the second cell can control the UE to transmit the D2D service dataon the third transmission carrier frequency.

Condition 2: The signal quality of the first cell is lower than anaccess threshold, signal quality of the second cell is higher than orequal to a reselection threshold, the UE can receive a third indicationmessage sent by the second cell, and an access priority of the thirdtransmission carrier frequency is higher than that of the secondtransmission carrier frequency. The third indication message indicatesthat the second cell can control the UE to transmit the D2D service dataon the third transmission carrier frequency.

The first indication information further includes a cell reselectionpriority.

In this scenario, the specified condition includes at least one of thefollowing.

Condition 1: Signal quality of the second cell is higher than or equalto a reselection threshold, a reselection priority of the second cell ishigher than or equal to that of the first cell, and the UE can receive asecond indication message sent by the second cell. The second indicationmessage indicates that the second cell can control the UE to transmitthe D2D service data on the second transmission carrier frequency.

Condition 2: Signal quality of the second cell is higher than the signalquality of the first cell, a reselection priority of the second cell ishigher than or equal to that of the first cell, and the UE can receive asecond indication message sent by the second cell. The second indicationmessage indicates that the second cell can control the UE to transmitthe D2D service data on the second transmission carrier frequency.

According to the technical solution proposed in Embodiment 1 of thepresent invention, the UE obtains the signal quality of the first celloperating on the first transmission carrier frequency. When the UEdetermines that the signal quality of the first cell is higher than thepreset threshold, and the UE receives the first indication informationsent by the first cell, the UE selects the first cell as the servingcell, and transmits the D2D service data on the second transmissioncarrier frequency. By receiving the first indication information, the UEcan select a transmission carrier frequency located at a differentfrequency to transmit the D2D service, so as to resolve a problem thatthe terminal cannot select a transmission carrier frequency located at adifferent frequency to transmit the D2D service data.

Embodiment 2

Embodiment 2 of the present invention provides a D2D servicetransmission method. As shown in FIG. 2b , a specific processingprocedure of the method is described as follows.

Step 31: UE obtains signal quality of a first cell operating on a firsttransmission carrier frequency.

The UE measures signal quality of a cell, to obtain the signal qualityof the first cell operating on the first transmission carrier frequency.

Step 32: When the UE determines that the signal quality of the firstcell is higher than a preset threshold, and the UE receives firstindication information sent by the first cell, the UE selects the firstcell as a serving cell.

The first indication information indicates that the first cell cancontrol the UE to transmit D2D service data on a second transmissioncarrier frequency, and the first transmission carrier frequency and thesecond transmission carrier frequency are located at differentfrequencies.

The UE may receive, in the following two manners, the first indicationinformation sent by the first cell:

In a first manner, the UE receives the first indication information thatis sent by the first cell by broadcasting system information.

In a second manner, the UE receives the first indication informationthat is sent by the first cell by using RRC-specific control signaling.

Step 33: The UE transmits D2D service data on a second transmissioncarrier frequency.

An LTE-based V2V communication scenario is used as an example fordetailed description.

The UE receives, using the first transmission carrier frequency, theindication information sent by the first cell, determines that the firstcell can control V2V service transmission on the second transmissioncarrier frequency, measures the signal quality of the first cell, anddetermines, according to a measurement result, whether the signalquality of the first cell is higher than or equal to the presetthreshold. If a determining result indicates that the signal quality ofthe first cell is higher than or equal to the preset threshold, the UEaccesses and camps on the first cell. That is, the UE selects the firstcell as the serving cell. The UE uses the second transmission carrierfrequency indicated by the indication information as a transmissioncarrier frequency for carrying a V2V service.

In the LTE-based V2V communication scenario, the transmission carrierfrequency for transmitting the V2V service and an LTE control carrierfrequency are located at two different frequencies. An existingmechanism for cell selection in a D2D service does not support resourceallocation for a V2V-specific transmission carrier frequency using theLTE control carrier frequency. Based on this, in the technical solutionproposed in Embodiment 2 of the present invention, the first celloperating on the first transmission carrier frequency sends theindication information. When the UE determines, according to thereceived indication information, that the signal quality of the firstcell is higher than the preset threshold, the UE selects the first cellas the serving cell, and transmits the V2V service on the secondtransmission carrier frequency.

Optionally, before the UE receives the first indication information sentby the first cell, the method further includes the following step.

The UE sends, to the first cell, a request message including frequencyinformation of a transmission carrier frequency for a D2D service inwhich the UE is interested. The first cell sends the first indicationinformation according to the request message.

In an embodiment, the first indication information includes frequencyinformation of a frequency of at least one second transmission carrierfrequency.

In an embodiment, frequency information that is of the secondtransmission carrier frequency and that is in the first indicationinformation sent by the first cell is included in the request message.

After the UE transmits the D2D service on the second transmissioncarrier frequency, the method further includes the following step.

The UE sends, to the first cell, a notification message includingfrequency information of the second transmission carrier frequency. Thenotification message informs the first cell that the UE uses the secondtransmission carrier frequency as a transmission carrier frequency fortransmitting the D2D service.

After the UE uses the first cell as the serving cell, the UE is notalways still. Therefore, as the UE moves, the UE may detect a secondcell whose signal quality is higher than that of the first cell, or theUE expects to transmit a D2D service using another transmission carrierfrequency. In this case, the UE needs to perform cell reselection.

Therefore, after the UE transmits the D2D service data on the secondtransmission carrier frequency, the method may further include thefollowing step.

The UE reselects a second cell for access.

The UE performs frequency scanning on a third transmission carrierfrequency, to determine the second cell. When the second cell meets aspecified condition, the UE reselects the second cell as the servingcell. The UE transmits D2D service data on a transmission carrierfrequency that is used to execute a D2D service and that can becontrolled by the second cell.

The specified condition includes at least one of the following.

Condition 1: Signal quality of the second cell is higher than or equalto a reselection threshold, and the UE can receive a second indicationmessage sent by the second cell, where the second indication messageindicates that the second cell can control the UE to transmit the D2Dservice data on the second transmission carrier frequency.

Condition 2: The signal quality of the first cell is lower than anaccess threshold, signal quality of the second cell is higher than orequal to a reselection threshold, and the UE can receive a secondindication message sent by the second cell, where the second indicationmessage indicates that the second cell can control the UE to transmitthe D2D service data on the second transmission carrier frequency.

Condition 3: The signal quality of the first cell is lower than anaccess threshold, signal quality of the second cell is higher than orequal to a reselection threshold, and the UE can receive a thirdindication message sent by the second cell, where the third indicationmessage indicates that the second cell can control the UE to transmitthe D2D service data on the third transmission carrier frequency.

The first indication information further includes an access priority ofa transmission carrier frequency used for transmitting the D2D service.In this scenario, the specified condition includes at least one of thefollowing.

Condition 1: Signal quality of the second cell is higher than or equalto a reselection threshold, the UE can receive a third indicationmessage sent by the second cell, and an access priority of the thirdtransmission carrier frequency is higher than that of the secondtransmission carrier frequency. The third indication message indicatesthat the second cell can control the UE to transmit the D2D service dataon the third transmission carrier frequency.

Condition 2: The signal quality of the first cell is lower than anaccess threshold, signal quality of the second cell is higher than orequal to a reselection threshold, the UE can receive a third indicationmessage sent by the second cell, and an access priority of the thirdtransmission carrier frequency is higher than that of the secondtransmission carrier frequency. The third indication message indicatesthat the second cell can control the UE to transmit the D2D service dataon the third transmission carrier frequency.

The first indication information further includes a cell reselectionpriority.

In this scenario, the specified condition includes at least one of thefollowing.

Condition 1: Signal quality of the second cell is higher than or equalto a reselection threshold, a reselection priority of the second cell ishigher than or equal to that of the first cell, and the UE can receive asecond indication message sent by the second cell. The second indicationmessage indicates that the second cell can control the UE to transmitthe D2D service data on the second transmission carrier frequency.

Condition 2: Signal quality of the second cell is higher than the signalquality of the first cell, a reselection priority of the second cell ishigher than or equal to that of the first cell, and the UE can receive asecond indication message sent by the second cell. The second indicationmessage indicates that the second cell can control the UE to transmitthe D2D service data on the second transmission carrier frequency.

Correspondingly, Embodiment 2 of the present invention further providesa D2D service transmission apparatus. As shown in FIG. 3, the apparatusincludes an obtaining module 301, a receiving module 302, a selectionmodule 303, and an execution module 304.

The obtaining module 301 is configured to obtain signal quality of afirst cell operating on a first transmission carrier frequency.

The receiving module 302 is configured to receive first indicationinformation sent by the first cell.

The selection module 303 is configured to: when it is determined thatthe signal quality of the first cell is higher than a preset threshold,and the first indication information sent by the first cell is received,select the first cell as a serving cell, where the first indicationinformation indicates that the first cell can control UE to transmitdevice-to-device D2D service data on a second transmission carrierfrequency. The first transmission carrier frequency and the secondtransmission carrier frequency are located at different frequencies.

The execution module 304 is configured to transmit the D2D service dataon the second transmission carrier frequency.

Specifically, the receiving module 302 is specifically configured toreceive the first indication information that is sent by the first cellby broadcasting system information; or receive the first indicationinformation that is sent by the first cell using radio resource controlRRC-specific control signaling.

The apparatus further includes a first sending module, configured tosend, to the first cell, a request message including frequencyinformation of a transmission carrier frequency for a D2D service inwhich the UE is interested. The first cell sends the first indicationinformation according to the request message.

Specifically, the first indication information received by the receivingmodule includes frequency information of a frequency of at least onesecond transmission carrier frequency.

Specifically, a frequency of the second transmission carrier frequencyselected by the selection module is included in the request message.

The apparatus further includes a second sending module, configured tosend, to the first cell, a notification message including frequencyinformation of the second transmission carrier frequency. Thenotification message informs the first cell that the UE uses the secondtransmission carrier frequency as a transmission carrier frequency fortransmitting the D2D service.

The apparatus further includes: a determining module, configured toperform frequency scanning on a third transmission carrier frequency, todetermine a second cell. The apparatus further includes a reselectionmodule, configured to: when the second cell meets a specified condition,reselect the second cell as the serving cell. The apparatus furtherincludes a transmission module, configured to transmit D2D service dataon a transmission carrier frequency that is used to execute a D2Dservice and that can be controlled by the second cell.

Specifically, the specified condition determined by the reselectionmodule includes at least one of the following: signal quality of thesecond cell is higher than or equal to a reselection threshold, and theUE can receive a second indication message sent by the second cell,where the second indication message indicates that the second cell cancontrol the UE to transmit the D2D service data on the secondtransmission carrier frequency; the signal quality of the first cell islower than an access threshold, signal quality of the second cell ishigher than or equal to a reselection threshold, and the UE can receivea second indication message sent by the second cell, where the secondindication message indicates that the second cell can control the UE totransmit the D2D service data on the second transmission carrierfrequency; or the signal quality of the first cell is lower than anaccess threshold, signal quality of the second cell is higher than orequal to a reselection threshold, and the UE can receive a thirdindication message sent by the second cell, where the third indicationmessage indicates that the second cell can control the UE to transmitthe D2D service data on the third transmission carrier frequency.

The first indication information further includes an access priority ofa transmission carrier frequency used for transmitting the D2D service.The specified condition determined by the reselection module includes atleast one of the following: signal quality of the second cell is higherthan or equal to a reselection threshold, the UE can receive a thirdindication message sent by the second cell, and an access priority ofthe third transmission carrier frequency is higher than that of thesecond transmission carrier frequency, where the third indicationmessage indicates that the second cell can control the UE to transmitthe D2D service data on the third transmission carrier frequency; or thesignal quality of the first cell is lower than an access threshold,signal quality of the second cell is higher than or equal to areselection threshold, the UE can receive a third indication messagesent by the second cell, and an access priority of the thirdtransmission carrier frequency is higher than that of the secondtransmission carrier frequency, where the third indication messageindicates that the second cell can control the UE to transmit the D2Dservice data on the third transmission carrier frequency.

The first indication information further includes a cell reselectionpriority. The specified condition determined by the reselection moduleincludes at least one of the following: signal quality of the secondcell is higher than or equal to a reselection threshold, a reselectionpriority of the second cell is higher than or equal to that of the firstcell, and the UE can receive a second indication message sent by thesecond cell, where the second indication message indicates that thesecond cell can control the UE to transmit the D2D service data on thesecond transmission carrier frequency; or signal quality of the secondcell is higher than the signal quality of the first cell, a reselectionpriority of the second cell is higher than or equal to that of the firstcell, and the UE can receive a second indication message sent by thesecond cell, where the second indication message indicates that thesecond cell can control the UE to transmit the D2D service data on thesecond transmission carrier frequency.

Correspondingly, Embodiment 2 of the present invention further providesa D2D service transmission device. As shown in FIG. 4, the deviceincludes a processor, an interface, and a bus, and the processor and theinterface are connected to each other by using the bus.

The processor 401 is configured to obtain signal quality of a first celloperating on a first transmission carrier frequency.

The processor may be a central processing unit (CPU), or a combinationof a CPU and a hardware chip. A signal processor may alternatively be anetwork processor (NP), a combination of a CPU and an NP, or acombination of an NP and a hardware chip.

The hardware chip may be one or a combination of the following: anapplication-specific integrated circuit (ASIC), a field-programmablegate array (FPGA), or a complex programmable logic device (CPLD).

The interface 402 is configured to receive first indication informationsent by the first cell.

The interface may be one or more of the following: a network interfacecontroller (NIC) providing a wired interface, such as an Ethernet NIC,where the Ethernet NIC can provide a copper interface and/or a fiberinterface; or an NIC providing a wireless interface, such as a wirelesslocal area network (WLAN) NIC.

The processor 401 is configured to: when it is determined that thesignal quality of the first cell is higher than a preset threshold, andthe first indication information sent by the first cell is received,select the first cell as a serving cell. The first indicationinformation indicates that the first cell can control UE to transmitdevice-to-device D2D service data on a second transmission carrierfrequency, and the first transmission carrier frequency and the secondtransmission carrier frequency are located at different frequencies. Theprocessor is also configured to transmit the D2D service data on thesecond transmission carrier frequency.

Specifically, the interface is configured to receive the firstindication information that is sent by the first cell by broadcastingsystem information; or receive the first indication information that issent by the first cell by using radio resource control (RRC)-specificcontrol signaling.

Specifically, the processor is further configured to send, to the firstcell using the interface, a request message including frequencyinformation of a transmission carrier frequency for a D2D service inwhich the UE is interested. The first cell sends the first indicationinformation according to the request message.

Specifically, the first indication information received by the interfaceincludes frequency information of a frequency of at least one secondtransmission carrier frequency.

Specifically, a frequency of the second transmission carrier frequencyselected by the processor is included in the request message.

Specifically, the interface is further configured to send, to the firstcell, a notification message including frequency information of thesecond transmission carrier frequency. The notification message informsthe first cell that the UE uses the second transmission carrierfrequency as a transmission carrier frequency for transmitting the D2Dservice.

Specifically, the processor is further configured to: perform frequencyscanning on a third transmission carrier frequency, to determine thesecond cell; when the second cell meets a specified condition, reselectthe second cell as the serving cell; and transmit D2D service data on atransmission carrier frequency that is used to execute a D2D service andthat can be controlled by the second cell.

Specifically, the specified condition determined by the processorincludes at least one of the following: signal quality of the secondcell is higher than or equal to a reselection threshold, and the UE canreceive a second indication message sent by the second cell, where thesecond indication message indicates that the second cell can control theUE to transmit the D2D service data on the second transmission carrierfrequency; the signal quality of the first cell is lower than an accessthreshold, signal quality of the second cell is higher than or equal toa reselection threshold, and the UE can receive a second indicationmessage sent by the second cell, where the second indication messageindicates that the second cell can control the UE to transmit the D2Dservice data on the second transmission carrier frequency; or the signalquality of the first cell is lower than an access threshold, signalquality of the second cell is higher than or equal to a reselectionthreshold, and the UE can receive a third indication message sent by thesecond cell, where the third indication message indicates that thesecond cell can control the UE to transmit the D2D service data on thethird transmission carrier frequency.

In an embodiment, the first indication information further includes anaccess priority of a transmission carrier frequency used fortransmitting the D2D service. The specified condition determined by theprocessor includes at least one of the following: signal quality of thesecond cell is higher than or equal to a reselection threshold, the UEcan receive a third indication message sent by the second cell, and anaccess priority of the third transmission carrier frequency is higherthan that of the second transmission carrier frequency, where the thirdindication message indicates that the second cell can control the UE totransmit the D2D service data on the third transmission carrierfrequency; or the signal quality of the first cell is lower than anaccess threshold, signal quality of the second cell is higher than orequal to a reselection threshold, the UE can receive a third indicationmessage sent by the second cell, and an access priority of the thirdtransmission carrier frequency is higher than that of the secondtransmission carrier frequency, where the third indication messageindicates that the second cell can control the UE to transmit the D2Dservice data on the third transmission carrier frequency.

The first indication information further includes a cell reselectionpriority. The specified condition determined by the processor includesat least one of the following: signal quality of the second cell ishigher than or equal to a reselection threshold, a reselection priorityof the second cell is higher than or equal to that of the first cell,and the UE can receive a second indication message sent by the secondcell, where the second indication message indicates that the second cellcan control the UE to transmit the D2D service data on the secondtransmission carrier frequency; or signal quality of the second cell ishigher than the signal quality of the first cell, a reselection priorityof the second cell is higher than or equal to that of the first cell,and the UE can receive a second indication message sent by the secondcell, where the second indication message indicates that the second cellcan control the UE to transmit the D2D service data on the secondtransmission carrier frequency.

Embodiment 3

Embodiment 3 of the present invention provides a D2D servicetransmission method. As shown in FIG. 5, a specific processing procedureof the method is described as follows.

Step 41: A first cell determines first indication information.

Step 42: The first cell sends the first indication information on afirst transmission carrier frequency.

The first indication information indicates that the first cell cancontrol UE to transmit device-to-device (D2D) service data on a secondtransmission carrier frequency. The UE determines, according to theindication information, to use the first cell as a serving cell andtransmit the D2D service data on the second transmission carrierfrequency.

The first cell may send the first indication information in thefollowing two manners:

In a first manner, the first cell sends the first indication informationby broadcasting system information.

In a second manner, the first cell sends the first indicationinformation by using RRC-specific control signaling.

The first indication information indicates that the first cell cancontrol the UE to transmit the D2D service data on the secondtransmission carrier frequency, and the first transmission carrierfrequency and the second transmission carrier frequency are located atdifferent frequencies.

The first transmission carrier frequency and the second transmissioncarrier frequency are located at different frequencies.

The method further includes the following step.

When the first cell determines that the UE transmits the D2D servicedata on the second transmission carrier frequency, the first cellallocates a D2D transmission resource on the second transmission carrierfrequency to the UE.

That the first cell sends the first indication information using a firsttransmission carrier frequency includes: the first cell sends theindication information by broadcasting system information; or the firstcell sends the first indication information using radio resource control(RRC)-specific control signaling.

Before the first cell sends the first indication information by usingthe first transmission carrier frequency, the method further includesthe following step.

The first cell receives a request message sent by the UE, and the firstcell sends the first indication information according to the requestmessage.

The request message includes frequency information of a transmissioncarrier frequency for a D2D service in which the UE is interested.

The first indication information that is sent by the first cell usingthe first transmission carrier frequency includes frequency informationof at least one second transmission carrier frequency.

Frequency information that is of the second transmission carrierfrequency and that is in the first indication information sent by thefirst cell is included in the request message.

The method further includes the following step.

The first cell receives a notification message that includes thefrequency information of the second transmission carrier frequency andthat is sent by the UE. The notification message informs the first cellthat the UE uses the second transmission carrier frequency as atransmission carrier frequency for transmitting the D2D service data.

Correspondingly, Embodiment 3 of the present invention further providesa D2D service transmission apparatus. As shown in FIG. 5, the apparatusincludes a determining module 501 and a sending module 502.

The determining module 501 is configured to determine first indicationinformation.

The sending module 502 is configured to send the first indicationinformation by using a first transmission carrier frequency. The firstindication information indicates that the first cell can control UE totransmit device-to-device (D2D) service data on a second transmissioncarrier frequency. The UE determines, according to the indicationinformation, to use the first cell as a serving cell and transmit theD2D service data on the second transmission carrier frequency, where thefirst transmission carrier frequency and the second transmission carrierfrequency are located at different frequencies.

The apparatus further includes: an execution module, configured to: whenit is determined that the UE transmits the D2D service data on thesecond transmission carrier frequency, allocate a D2D transmissionresource on the second transmission carrier frequency to the UE.

In an embodiment, the sending module is configured to send theindication information by broadcasting system information; or send thefirst indication information using radio resource control (RRC)-specificcontrol signaling.

The apparatus further includes a first receiving module, configured toreceive a request message sent by the UE. The request message includesfrequency information of a transmission carrier frequency for a D2Dservice in which the UE is interested. The sending module is configuredto send the first indication information according to the requestmessage.

Specifically, the first indication information that is sent by thesending module using the first transmission carrier frequency includesfrequency information of at least one second transmission carrierfrequency.

In an embodiment, frequency information that is of the secondtransmission carrier frequency and that is in the first indicationinformation sent by the sending module is included in the requestmessage.

The apparatus further includes a second receiving module, configured toreceive a notification message that includes the frequency informationof the second transmission carrier frequency and that is sent by the UE.The notification message is used to inform the first cell that the UEuses the second transmission carrier frequency as a transmission carrierfrequency for transmitting the D2D service data.

Correspondingly, Embodiment 3 of the present invention further providesa D2D service transmission device. For a schematic structural diagram ofthe device, refer to FIG. 4. The device includes a processor and aninterface, and the processor and the interface are connected to eachother by using a bus.

The processor is configured to send first indication information basedon a first transmission carrier frequency using the interface, where thefirst indication information indicates that the first cell can controlUE to transmit device-to-device D2D service data on a secondtransmission carrier frequency. The UE determines, according to theindication information, to use the first cell as a serving cell andtransmit the D2D service data on the second transmission carrierfrequency, where the first transmission carrier frequency and the secondtransmission carrier frequency are located at different frequencies.

The processor is further configured to: when it is determined that theUE transmits the D2D service data on the second transmission carrierfrequency, allocate a D2D transmission resource on the secondtransmission carrier frequency to the UE.

The interface is configured to send the indication information bybroadcasting system information; or send the first indicationinformation using radio resource control (RRC)-specific controlsignaling.

The interface may be further configured to receive a request messagesent by the UE, where the request message includes frequency informationof a transmission carrier frequency for a D2D service in which the UE isinterested; and send the first indication information according to therequest message.

The first indication information that is sent based on the firsttransmission carrier frequency using the interface includes frequencyinformation of at least one second transmission carrier frequency.

The frequency information that is of the second transmission carrierfrequency and that is in the first indication information sent by theinterface is included in the request message.

The interface is further configured to receive a notification messagethat includes the frequency information of the second transmissioncarrier frequency and that is sent by the UE, where the notificationmessage informs the first cell that the UE uses the second transmissioncarrier frequency as a transmission carrier frequency for transmittingthe D2D service data.

A person skilled in the art should understand that the embodiments ofthe present invention may be provided as a method, an apparatus(device), or a computer program product. Therefore, the presentinvention may use a form of hardware only embodiments, software onlyembodiments, or embodiments with a combination of software and hardware.Moreover, the present invention may use a form of a computer programproduct that is implemented on one or more computer-usable storage media(including but not limited to a magnetic disk storage, a CD-ROM, anoptical memory, and the like) that include computer-usable program code.

The present invention is described with reference to the flowchartsand/or block diagrams of the method, the apparatus (device), and thecomputer program product according to the embodiments of the presentinvention. It should be understood that computer program instructionsmay be used to implement each process and/or each block in theflowcharts and/or the block diagrams and a combination of a processand/or a block in the flowcharts and/or the block diagrams. Thesecomputer program instructions may be provided for a general-purposecomputer, a special-purpose computer, an embedded processor, or aprocessor of another programmable data processing device to generate amachine, so that the instructions executed by a computer or theprocessor of the another programmable data processing device generate anapparatus for implementing a specific function in one or more processesin the flowcharts and/or in one or more blocks in the block diagrams.

These computer program instructions may alternatively be stored in acomputer readable memory that can instruct the computer or any otherprogrammable data processing device to work in a specific manner, sothat the instructions stored in the computer readable memory generate anartifact that includes an instruction apparatus. The instructionapparatus implements a specific function in one or more processes in theflowcharts and/or in one or more blocks in the block diagrams.

These computer program instructions may alternatively be loaded onto acomputer or another programmable data processing device, so that aseries of operations and steps are performed on the computer or theanother programmable device, thereby generating computer-implementedprocessing. Therefore, the instructions executed on the computer or theanother programmable device provide steps for implementing a specificfunction in one or more processes in the flowcharts and/or in one ormore blocks in the block diagrams.

Although some preferred embodiments of the present invention have beendescribed, persons skilled in the art can make changes and modificationsto these embodiments once they learn the basic inventive concept.Therefore, the following claims are intended to be construed as to coverthe preferred embodiments and all changes and modifications fallingwithin the scope of the present invention.

Obviously, a person skilled in the art can make various modificationsand variations to the present invention without departing from thespirit and scope of the present invention. The present invention isintended to cover these modifications and variations provided that theyfall within the scope of the claims and their equivalent technologies ofthe present invention.

What is claimed is:
 1. A method, comprising: obtaining, by userequipment (UE), signal quality of a first cell, wherein the first celloperates on a first transmission carrier frequency, and the first cellis served by a base station; when the UE determines that the signalquality of the first cell is higher than a preset threshold, and whenthe UE receives first indication information sent by the base stationthrough the first cell, selecting, by the UE, the first cell as aserving cell, wherein the first indication information indicates thatthe base station can control the UE to transmit device-to-device (D2D)service data using a second transmission carrier frequency, and thefirst transmission carrier frequency and the second transmission carrierfrequency are different frequencies; and transmitting, by the UE, theD2D service data using the second transmission carrier frequency.
 2. Themethod according to claim 1, wherein the serving cell supports a D2Dservice.
 3. The method according to claim 1, wherein the UE is asynchronization source on the second transmission carrier frequency, andthe UE sets a coverage identifier of the UE to in-coverage.
 4. Themethod according to claim 1, wherein the UE receiving first indicationinformation sent by the base station through the first cell comprises:receiving, by the UE, the first indication information, wherein thefirst indication information is sent by the base station through thefirst cell by broadcasting system information comprising the firstindication information; or receiving, by the UE, the first indicationinformation, wherein the first indication information is sent by thebase station through the first cell using radio resource control (RRC)specific control signaling.
 5. The method according to claim 1, whereinthe first indication information comprises frequency information of afrequency of the second transmission carrier frequency.
 6. A method,comprising: sending, by a base station through a first cell, firstindication information to a user equipment (UE), wherein the firstindication information is sent using a first transmission carrierfrequency, the first indication information indicates that the basestation can control the UE to transmit device-to-device (D2D) servicedata using a second transmission carrier frequency, the first indicationinformation further indicates the first cell on the first transmissioncarrier frequency served by the base station being a serving cell, andthe first indication information further indicates the secondtransmission carrier frequency to be used by the UE to transmit the D2Dservice data, and wherein the first transmission carrier frequency andthe second transmission carrier frequency are different frequencies. 7.The method according to claim 6, wherein the serving cell supports a D2Dservice.
 8. The method according to claim 6, wherein sending, by thebase station through the first cell, the first indication informationusing the first transmission carrier frequency comprises: sending, bythe base station using the first cell, the first indication informationby broadcasting system information comprising the first indicationinformation; or sending, by the base station through the first cell, thefirst indication information using radio resource control (RRC) specificcontrol signaling.
 9. The method according to claim 6, wherein the firstindication information that is sent by the base station through thefirst cell using the first transmission carrier frequency comprisesfrequency information of the second transmission carrier frequency. 10.A device, comprising: a processor, configured to obtain signal qualityof a first cell, wherein the first cell operates on a first transmissioncarrier frequency, and the first cell is served by a base station; andan interface, configured to receive first indication information sent bythe base station through the first cell; wherein the processor isfurther configured to: when it is determined that the signal quality ofthe first cell is higher than a preset threshold, and when the firstindication information sent by the base station through the first cellis received, select the first cell as a serving cell, wherein the firstindication information indicates that the base station can control thedevice to transmit device-to-device (D2D) service data on a secondtransmission carrier frequency, and the first transmission carrierfrequency and the second transmission carrier frequency are located atdifferent frequencies; and transmit the D2D service data on the secondtransmission carrier frequency.
 11. The device according to claim 10,wherein the serving cell supports the D2D service.
 12. The deviceaccording to claim 10, wherein the device is a synchronization source onthe second transmission carrier frequency, and the device sets acoverage identifier to in-coverage.
 13. The device according to claim10, wherein the interface is configured to: receive the first indicationinformation that is sent by the base station through the first cell,wherein the first indication information is sent by the base station bybroadcasting system information comprising the first indicationinformation; or receive the first indication information that is sent bythe base station through the first cell, wherein the first indicationinformation is sent by the base station using radio resource control(RRC) specific control signaling.
 14. The device according to claim 10,wherein the first indication information received by the interfacecomprises frequency information of a frequency of the secondtransmission carrier frequency.
 15. A device, comprising: a processor;and an interface; wherein the processor is configured to: send firstindication information on a first transmission carrier frequency usingthe interface, wherein the first indication information indicates thatthe device can control user equipment (UE) to transmit device-to-device(D2D) service data on a second transmission carrier frequency, the firstindication information further indicates a first cell on the firsttransmission carrier frequency served by the device as being a servingcell, and the first indication information further indicates the secondtransmission carrier frequency, wherein the first transmission carrierfrequency and the second transmission carrier frequency are differentfrequencies.
 16. The device according to claim 15, wherein the servingcell supports a D2D service.
 17. The device according to claim 16,wherein the interface is configured to: send the first indicationinformation by broadcasting system information comprising the firstindication information; or send the first indication information usingradio resource control (RRC) specific control signaling.
 18. The deviceaccording to claim 16, wherein the first indication information that issent on the first transmission carrier frequency using the interfacecomprises frequency information of the second transmission carrierfrequency.